https://github.com/ilovepi created
https://github.com/llvm/llvm-project/pull/82400
ARM's Clang and GCC embedded compilers default to allowing unaligned
access for ARMv7+. This patch changes the Clang driver default to match.
Users can opt out with `-mno-unaligned-access`.
Fixes #59560
>From 20634c2f54ae667ee8374d12e58e582aa6cdd051 Mon Sep 17 00:00:00 2001
From: Paul Kirth <paulki...@google.com>
Date: Tue, 20 Feb 2024 10:34:57 -0800
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
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Created using spr 1.3.4
---
clang/lib/Driver/ToolChains/Arch/ARM.cpp | 14 ++++++--------
clang/test/Driver/arm-alignment.c | 8 ++++++++
2 files changed, 14 insertions(+), 8 deletions(-)
diff --git a/clang/lib/Driver/ToolChains/Arch/ARM.cpp
b/clang/lib/Driver/ToolChains/Arch/ARM.cpp
index e6ee2f88a84edf..3bf6056f0c3ecc 100644
--- a/clang/lib/Driver/ToolChains/Arch/ARM.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/ARM.cpp
@@ -895,20 +895,18 @@ llvm::ARM::FPUKind arm::getARMTargetFeatures(const Driver
&D,
// defaults this bit to 0 and handles it as a system-wide (not
// per-process) setting. It is therefore safe to assume that ARMv7+
// Linux targets support unaligned accesses. The same goes for NaCl
- // and Windows.
- //
- // The above behavior is consistent with GCC.
+ // and Windows. However, ARM's forks of GCC and Clang both allow
+ // unaligned accesses by default for all targets. We follow this
+ // behavior and enable unaligned accesses by default for ARMv7+ targets.
+ // Users can disable behavior via compiler options (-mno-unaliged-access).
+ // See https://github.com/llvm/llvm-project/issues/59560 for more info.
int VersionNum = getARMSubArchVersionNumber(Triple);
if (Triple.isOSDarwin() || Triple.isOSNetBSD()) {
if (VersionNum < 6 ||
Triple.getSubArch() == llvm::Triple::SubArchType::ARMSubArch_v6m)
Features.push_back("+strict-align");
- } else if (Triple.isOSLinux() || Triple.isOSNaCl() ||
- Triple.isOSWindows()) {
- if (VersionNum < 7)
+ } else if (VersionNum < 7)
Features.push_back("+strict-align");
- } else
- Features.push_back("+strict-align");
}
// llvm does not support reserving registers in general. There is support
diff --git a/clang/test/Driver/arm-alignment.c
b/clang/test/Driver/arm-alignment.c
index 9177b625729b85..6d0084451e82c7 100644
--- a/clang/test/Driver/arm-alignment.c
+++ b/clang/test/Driver/arm-alignment.c
@@ -22,6 +22,14 @@
// RUN: %clang -target armv7-windows -### %s 2> %t
// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
+/// Ensure that by default before ARMv7 we default to +strict-align
+// RUN: %clang -target armv6 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
+
+/// After ARMv7 by default we allow unaligned accesses for all targets
+// RUN: %clang -target armv7 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
+
// RUN: %clang --target=aarch64 -munaligned-access -### %s 2> %t
// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-AARCH64 < %t %s
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